Transmissions are commonly used to couple driving sources such as motors and the like to the drive train of a system or to the wheels of an automobile or bicycle. Transmissions accomplish a gearing up or a gearing down between the drive source and the driven member by varying the relative rotation between the driving member and the driven member through a series of ratios or "gears," the ratio being varied stepwise or continuously over some predetermined range.
Various previous attempts at automatic transmissions have involved very complex arrangements of torque converters, gears, etc. which caused the transmission to shift between a few preselected drive ratios at predetermined points. Typically, these points are at clearly defined occurrences, e.g., specific rotational speeds of the driving or driven member.
Chain drive systems are particularly useful in light duty applications such as bicycles and motorcycles. Potentially, they would also be particularly adaptable to small cars, particularly ones employing front wheel drive and having a transversely mounted engine. However, both manual and automatic shifting transmissions available for chain drive systems have been a major drawback or totally unacceptable in applications.
Some chain drive transmission mechanisms have used sprocket wheels of graduated dimensions together with a deraileur system to shift the chain from one sprocket wheel to the next. These systems are typically not reliable, require precise and frequent adjustment, do not shift well under a heavy load and the missing of a sprocket wheel during a shift results in a catastrophic failure of the system, e.g., the chain falling between the sprocket wheels and jumping the mechanism.
Therefore, while chain drive mechanisms are commonly in use, the aforesaid disadvantages of chain drive mechanisms have limited their use primarily to those applications where a variable ratio transmission is not necessary; where the deraileur shifting system is acceptable, e.g., such as bicycles; or where a conventional transmission is inserted elsewhere in the system. An example of the latter is those bicycles or motorcycles wherein a transmission is placed within the hub of the driven wheel and manually controlled from the handlebars.
Note that while the above solutions have been adequate in their applications, there has been up to this time no simple and dependable chain drive automatic transmissions which were continuously variable over a range of drive ratios and which provided automatic variation of the drive ratio in response to the torque applied to the system.